High-strength microwave antenna assemblies and methods of use

ABSTRACT

High-strength microwave antenna assemblies and methods of use are described herein. The microwave antenna has a radiating portion connected by a feedline to a power generating source, e.g., a generator. The antenna is a dipole antenna with the distal end of the radiating portion being tapered and terminating at a tip to allow for direct insertion into tissue. The antenna can be used individually or in combination with multiple antennas to create a combined ablation field. When multiple antennas are used, microwave energy can be applied simultaneously to all the antennas or sequentially between the antennas. Furthermore, to facilitate positioning the antennas in or near the tissue to be treated, RF energy may be applied at the tip of the antenna to assist in cutting through the tissue.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation-in-part of U.S. patentapplication Ser. No. 10/052,848 filed Nov. 2, 2001, which isincorporated herein by reference in its entirety.

FIELD OF THE INVENTION

[0002] The invention relates generally to microwave antenna probes andmethods of their use which may be used in tissue ablation applications.More particularly, the invention relates to microwave antennas which maybe inserted directly into tissue for diagnosis and treatment ofdiseases.

BACKGROUND OF THE INVENTION

[0003] In the treatment of diseases such as cancer, certain types ofcancer cells have been found to denature at elevated temperatures whichare slightly lower than temperatures normally injurious to healthycells. These types of treatments, known generally as hyperthermiatherapy, typically utilize electromagnetic radiation to heat diseasedcells to temperatures above 41° C. while maintaining adjacent healthycells at lower temperatures where irreversible cell destruction will notoccur. Other procedures utilizing electromagnetic radiation to heattissue also include ablation and coagulation of the tissue. Suchmicrowave ablation procedures, e.g., such as those performed formenorrhagia, are typically done to ablate and coagulate the targetedtissue to denature or kill it. Many procedures and types of devicesutilizing electromagnetic radiation therapy are known in the art. Suchmicrowave therapy is typically used in the treatment of tissue andorgans such as the prostate, heart, and liver.

[0004] One non-invasive procedure generally involves the treatment oftissue (e.g., a tumor) underlying the skin via the use of microwaveenergy. The microwave energy is able to non-invasively penetrate theskin to reach the underlying tissue. However, this non-invasiveprocedure may result in the unwanted heating of healthy tissue. Thus,the non-invasive use of microwave energy requires a great deal ofcontrol. This is partly why a more direct and precise method of applyingmicrowave radiation has been sought.

[0005] Presently, there are several types of microwave probes in use,e.g., monopole, dipole, and helical. One type is a monopole antennaprobe, which consists of a single, elongated microwave conductor exposedat the end of the probe. The probe is sometimes surrounded by adielectric sleeve. The second type of microwave probe commonly used is adipole antenna, which consists of a coaxial construction having an innerconductor and an outer conductor with a dielectric separating a portionof the inner conductor and a portion of the outer conductor. In themonopole and dipole antenna probe, microwave energy generally radiatesperpendicularly from the axis of the conductor.

[0006] The typical microwave antenna has a long, thin inner conductorwhich extends along the axis of the probe and is surrounded by adielectric material and is further surrounded by an outer conductoraround the dielectric material such that the outer conductor alsoextends along the axis of the probe. In another variation of the probewhich provides for effective outward radiation of energy or heating, aportion or portions of the outer conductor can be selectively removed.This type of construction is typically referred to as a “leakywaveguide” or “leaky coaxial” antenna. Another variation on themicrowave probe involves having the tip formed in a uniform spiralpattern, such as a helix, to provide the necessary configuration foreffective radiation. This variation can be used to direct energy in aparticular direction, e.g., perpendicular to the axis, in a forwarddirection (i.e., towards the distal end of the antenna), or acombination thereof.

[0007] Invasive procedures and devices have been developed in which amicrowave antenna probe may be either inserted directly into a point oftreatment via a normal body orifice or percutaneously inserted. Suchinvasive procedures and devices potentially provide better temperaturecontrol of the tissue being treated. Because of the small differencebetween the temperature required for denaturing malignant cells and thetemperature injurious to healthy cells, a known heating pattern andpredictable temperature control is important so that heating is confinedto the tissue to be treated. For instance, hyperthermia treatment at thethreshold temperature of about 41.5° C. generally has little effect onmost malignant growths of cells. However, at slightly elevatedtemperatures above the approximate range of 43° C. to 45° C., thermaldamage to most types of normal cells is routinely observed; accordingly,great care must be taken not to exceed these temperatures in healthytissue.

[0008] However, many types of malignancies are difficult to reach andtreat using non-invasive techniques or by using invasive antenna probesdesigned to be inserted into a normal body orifice, i.e., a body openingwhich is easily accessible. These types of conventional probes may bemore flexible and may also avoid the need to separately sterilize theprobe; however, they are structurally weak and typically require the useof an introducer or catheter to gain access to within the body.Moreover, the addition of introducers and catheters necessarily increasethe diameter of the incision or access opening into the body therebymaking the use of such probes more invasive and further increasing theprobability of any complications that may arise.

[0009] Structurally stronger invasive probes exist and are typicallylong, narrow, needle-like antenna probes which may be inserted directlyinto the body tissue to directly access a site of a tumor or othermalignancy. Such rigid probes generally have small diameters which aidnot only in ease of use but also reduce the resulting trauma to thepatient. A convenience of rigid antenna probes capable of directinsertion into tissue is that the probes may also allow for alternateadditional uses given different situations. However, such rigid,needle-like probes commonly experience difficulties in failing toprovide uniform patterns of radiated energy; they fail to provideuniform heating axially along and radially around an effective length ofthe probe; and it is difficult to otherwise control and direct theheating pattern when using such probes.

[0010] Accordingly, there remains a need for a microwave antenna probewhich overcomes the problems discussed above. There also exists a needfor a microwave antenna probe which is structurally robust enough fordirect insertion into tissue without the need for additional introducersor catheters and which produces a controllable and predictable heatingpattern.

SUMMARY OF THE INVENTION

[0011] A microwave antenna assembly which is structurally robust enoughfor unaided direct insertion into tissue is described herein. Themicrowave antenna assembly is generally comprised of a radiating portionwhich may be connected to a feedline (or shaft) which in turn may beconnected by a cable to a power generating source such as a generator.The microwave assembly may be a monopole microwave antenna assembly butis preferably a dipole assembly. The distal portion of the radiatingportion preferably has a tapered end which terminates at a tip to allowfor the direct insertion into tissue with minimal resistance. Theproximal portion is located proximally of the distal portion, and ajunction member is preferably located between both portions.

[0012] The adequate rigidity necessary for unaided direct insertion ofthe antenna assembly into tissue, e.g., percutaneously, preferably comesin part by a variety of different methods. Some of the methods includeassembling the antenna under a pre-stressed condition prior to insertioninto tissue. This may be accomplished in part by forcing an innerconductor, which runs longitudinally through the assembly, into atensile condition by preferably affixing the inner conductor distal endto the distal radiating portion of the antenna assembly. Another methodincludes configuring the proximal and distal radiating portions of theantenna to mechanically fasten to each other. That is, the proximal anddistal radiating portions may be configured to “screw” into one anotherdirectly or to a junction member located between the two portions andwhich is threaded such that the portions each screw onto the junctionmember separately.

[0013] Another method includes attaching the proximal and distalradiating portions together by creating overlapping or interfittingjoints. In this variation, either the proximal or the distal radiatingportion may be configured to create an overlapping joint by interfittingwith each other through a variety of joints. For instance, the distalportion may be configured to intimately fit within a receiving cavity orchannel at the distal end of the proximal portion. The two portions mayalso be configured to have a number of pins or conical members extendingto join the two. Alternatively, the two portions may be frictionallyinterfitted by an interference fitted joint; or depressible/retractableprojections may be disposed on either portion to interfit withcorresponding depressions in the opposite portion.

[0014] To further aid in strengthening the antenna assemblies, a varietyof methods may also be used for attaching the tip or distal portion. Forinstance, a variation may have a distal portion which may screw onto athreaded inner conductor or another variation may have an innerconductor having an anchoring element capable of holding the innerconductor within a splittable distal portion. Furthermore, amulti-sectioned distal portion may also be utilized for first attachingan inner conductor to the distal portion and then assembling the distalportion with additional variable sections. In many of the variationsdescribed herein, it may be preferable to have a dielectric materialapplied as a layer or coating between the two radiating portions.

[0015] Affixing the inner conductor within the distal radiating portionmay be accomplished in a variety of ways, for instance, welding,brazing, soldering, or through the use of adhesives. Forcing the innerconductor into a tensile condition helps to force the outer diameter ofthe antenna into a compressive state. This bi-directional stress statein turn aids in rigidizing the antenna assembly.

[0016] To enable a compressive state to exist near the outer diameter,the junction member between the distal and the proximal radiatingportions in some of the variations is preferably made from asufficiently hard dielectric material, e.g., ceramic materials. Thehardness of the junction member aids in transferring the compressiveforces through the antenna assembly without buckling or kinking duringantenna insertion into tissue. Furthermore, materials such as ceramicgenerally have mechanical properties where fracturing or cracking in thematerial is more likely to occur under tensile loading conditions.Accordingly, placing a junction under pre-stressed conditions,particularly a junction made of ceramic, may aid in preventingmechanical failure of the junction if the antenna were to incur bendingmoments during insertion into tissue which could subject portions of thejunction under tensile loads. The junction member may also be made intouniform or non-uniform, e.g., stepped, shapes to accommodate varyingantenna assembly designs.

[0017] Moreover, to improve the energy focus of an antenna assembly, anelectrical choke may also be used in any of the variations describedherein to contain returning currents to the distal end of the antennaassembly. Generally, the choke may be disposed on top of a dielectricmaterial on the antenna proximally of the radiating section. The chokeis preferably comprised of a conductive layer and may be further coveredby a tubing or coating to force the conductive layer to conform to theunderlying antenna.

[0018] Additionally, variations on the choke, the tubing or coating, anysealant layers, as well as other layers which may be disposed over theantenna assembly may be used. Certain layers, e.g., a heatshrink layerdisposed over the antenna assembly, may have wires or strands integratedwithin the layer to further strengthen the antenna assembly. Kevlarwires, for instances, may be integrally formed into the layer andoriented longitudinally with the antenna axis to provide additionalstrength.

[0019] In use, to facilitate insertion of a microwave antenna intotissue, various ablative tips may be utilized. For example, onevariation may utilize an antenna which is insulated along its lengthexcept at the distal tip. The distal tip may be energized by RF energydelivered through, e.g., the inner conductor. During antenna deployment,RF energy may be applied continuously or selectively to the exposeddistal tip to facilitate antenna insertion by using the RF energized tipto cut through the tissue as the antenna is advanced. Another variationmay utilize an inner conductor which may be slidably disposed within alumen through the antenna. As the antenna is advanced through thetissue, when resistance is encountered the inner conductor, which may beattached to an RF generator, may be advanced distally within the lumento extend at least partially out of the distal tip of the antenna. RFenergy may then be applied such that the energized inner conductorfacilitates antenna advancement by cutting the tissue.

[0020] Any of the antenna variations described herein may be utilized ina variety of methods to effect tissue treatment. For instance, in onevariation, a single antenna may be used to treat the tissue in a singlelocation. In another variation, a single antenna may be positionedwithin a first region of tissue for treatment, then the antenna may beremoved and repositioned in another region of tissue, and so on for anynumber of times and positions, until satisfactory treatment is effected.In yet another variation, multiple antennas may be used simultaneouslyto effect treatment to a region of tissue. In this variation, thesimultaneous use of multiple antennas may effectively create a combinedtreatment or ablation field which is larger than an ablation field thata single antenna used alone or sequentially may create. In yet anothervariation, multiple antennas may be used together but the power providedto each may be cycled between the antennas in an unlimited number ofcombinations through the use of multiplexing methods. Such a use mayreduce the overall power of the system for treatment while effectivelytreating the tissue region of interest.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021]FIG. 1 shows a representative diagram of a variation of amicrowave antenna assembly.

[0022]FIGS. 2A and 2B show an end view and a cross-sectional view,respectively, of a conventional dipole microwave antenna assembly.

[0023]FIG. 3 shows an exploded cross-sectional view of a variation on apre-stressed antenna assembly.

[0024]FIG. 4 shows the assembled pre-stressed antenna assembly of FIG. 3and the directions of stress loads created within the assembly.

[0025]FIG. 5 shows another variation of pre-stressed antenna assemblyhaving a sharpened distal tip.

[0026]FIG. 6 shows an exploded cross-sectional view of another variationon pre-stressed antenna assembly having a non-uniform junction member.

[0027]FIG. 7 shows an exploded cross-sectional view of yet anothervariation on pre-stressed antenna assembly having an access channeldefined along the side of the antenna.

[0028]FIG. 8 shows a pre-stressed monopole variation of a microwaveantenna assembly.

[0029]FIG. 9A shows a side view of another variation on a pre-stressedantenna assembly having an electrical choke.

[0030]FIG. 9B shows a cross-sectional view of the assembly of FIG. 9A.

[0031]FIG. 10 shows a detailed view of a variation on the radiatingportion of FIG. 9B.

[0032]FIG. 11 shows a detailed view of a variation on the transitionfrom the radiating portion to the electrical choke of FIG. 9B.

[0033]FIG. 12 shows a detailed view of a variation on the differentlayers within the electrical choke of FIG. 9B.

[0034]FIG. 13 shows a detailed view of a variation on the feedline ofFIG. 9B.

[0035]FIG. 14 shows an isometric view of a sectioned antenna assemblyhaving a layer, such as a heatshrink layer, formed with wires or strandslongitudinally orientated within the layer.

[0036]FIG. 15 shows an exploded cross-sectional side view of a variationof the microwave antenna assembly having a mechanically threadedinterface.

[0037]FIG. 16 shows an exploded cross-sectional side view of anothervariation of the antenna assembly also having a mechanically threadedinterface.

[0038]FIG. 17 shows a cross-sectional side view of a crimped oroverlapping variation of the antenna assembly.

[0039]FIG. 18 shows a cross-sectional side view of an antenna assemblywhere the proximal portion may be configured to receive and hold thedistal portion in an overlapping joint.

[0040]FIG. 19 shows an exploded cross-sectional side view of a variationof the antenna assembly having an interfitting joint with an overlappingjunction member.

[0041]FIG. 20 shows a cross-sectional side view of an antenna assemblywith two variations on the distal portion joint for interfitting withthe proximal portion.

[0042]FIGS. 21A and 21B show the corresponding end views of the proximalportion from FIG. 20 with two variations for interfitting with thedistal portions.

[0043]FIG. 22 shows an exploded cross-sectional side view of anothervariation where the antenna may be assembled using overlappinginterference fitted joints.

[0044]FIG. 23 shows another variation in an exploded cross-sectionalside view of an antenna assembled via a junction member and multiplepins.

[0045]FIG. 24 shows an exploded cross-sectional side view of anothervariation in which the distal portion may have a plurality ofprojections which interfit with corresponding depressions within theproximal portion.

[0046]FIG. 25 shows another variation in which the projections and theircorresponding interfitting depressions may have corresponding accesschannels in the proximal portion through which the distal portion may bewelded, soldered, brazed, or adhesively affixed to the proximal portion.

[0047]FIG. 26 shows a side view of a variation on attaching the distalto the inner conductor by a screw-on method.

[0048]FIG. 27 shows an isometric exploded view of another variation onattaching the distal portion by anchoring the inner conductor within asplittable distal portion.

[0049]FIG. 28 shows an exploded side view of a multi-sectioned distalvariation.

[0050]FIG. 29 shows a cross-sectioned side view of an alternative distalhaving an arcuate or curved sloping face to facilitate antenna assemblyas entry into tissue.

[0051]FIG. 30 shows an assembled cross-sectional side view of arepresentative antenna assembly having a constant diameter over theproximal and distal portions.

[0052]FIG. 31 shows the antenna of FIG. 30 but with the distal portionhaving a diameter larger than the diameter of the proximal portion.

[0053]FIG. 32 shows the antenna of FIG. 30 but with the distal portiondiameter smaller than the diameter of the proximal portion.

[0054]FIG. 33 shows an antenna variation which may be used with RFenergy to facilitate insertion into tissue or to cut through obstructivetissue.

[0055]FIGS. 34A and 34B show another variation which may also be used todeliver RF energy.

[0056]FIGS. 35A and 35B show an isometric and end view, respectively, ofone variation in using a single antenna.

[0057]FIGS. 36A and 36B show an isometric and end view, respectively, ofanother variation in using a single antenna in multiple positions.

[0058]FIGS. 37A and 37B show an isometric and end view, respectively, ofyet another variation in using multiple antennas in multiple positions.

[0059]FIG. 38 shows a schematic illustration of a variation for achannel splitter assembly for creating multiple channels using a singlesource.

DETAILED DESCRIPTION OF THE INVENTION

[0060] In invasively treating diseased areas of tissue in a patient,trauma may be caused to the patient resulting in pain and othercomplications. Various microwave antenna assemblies, as describedherein, are less traumatic than devices currently available and asdescribed in further detail below, methods of manufacturing such devicesare also described. Generally, an apparatus of the present inventionallows for the direct insertion of a microwave antenna into tissue forthe purposes of diagnosis and treatment of disease. FIG. 1 shows arepresentative diagram of a variation of a microwave antenna assembly 10of the present invention. The antenna assembly 10 is generally comprisedof radiating portion 12 which may be connected by feedline 14 (or shaft)via cable 15 to connector 16, which may further connect the assembly 10to a power generating source 28, e.g., a generator. Assembly 10, asshown, is a dipole microwave antenna assembly, but other antennaassemblies, e.g., monopole or leaky wave antenna assemblies, may alsoutilize the principles set forth herein. Distal portion 20 of radiatingportion 12 preferably has a tapered end 24 which terminates at a tip 26to allow for insertion into tissue with minimal resistance. In thosecases where the radiating portion 12 is inserted into a pre-existingopening, tip 26 may be rounded or flat.

[0061] In some applications a microwave antenna requires adequatestructural strength to prevent bending of the antenna, e.g., where theantenna is directly inserted into tissue, where the antenna undergoesbending moments after insertion, etc. Accordingly, there are variousconfigurations to increase the antenna strength without compromisingdesirable radiative properties and the manufacturability of such anantenna. One configuration involves placing the antenna assembly under acompressive load to stiffen the radiating portions. Anotherconfiguration involves mechanically fastening, e.g., in a screw-likemanner, the radiating portions together to provide a joint which willwithstand bending moments. A further configuration may also involvecreating overlapping joints between the radiating portions of theantenna assembly to provide a high strength antenna. Furthermore,alternate configurations of attaching a distal tip or distal radiatingportion to an antenna may be utilized to further increase the antennastrength.

[0062] Antenna Assembly Via Compression

[0063] Generally, the antenna assembly 10 in FIG. 1 shows a variationwhere a compressive load may be used to increase antenna strength.Proximal portion 22 is located proximally of distal portion 20, andjunction member 18 is preferably located between both portions such thata compressive force is applied by distal and proximal portions 20, 22upon junction member 18. Placing distal and proximal portions 20, 22 ina pre-stressed condition prior to insertion into tissue enables assembly10 to maintain a stiffness that is sufficient to allow for unaidedinsertion into the tissue while maintaining a minimal antenna diameter,as described in detail below.

[0064] Feedline 14 may electrically connect antenna assembly 10 viacable 15 to generator 28 and usually comprises a coaxial cable made of aconductive metal which may be semi-rigid or flexible. Feedline 14 mayalso have a variable length from a proximal end of radiating portion 12to a distal end of cable 15 ranging between about 1 to 10 inches. Mostfeedlines may be constructed of copper, gold, or other conductive metalswith similar conductivity values, but feedline 14 is preferably made ofstainless steel. The metals may also be plated with other materials,e.g., other conductive materials, to improve their properties, e.g., toimprove conductivity or decrease energy loss, etc. A feedline 14, suchas one made of stainless steel, preferably has an impedance of about 50Ω and to improve its conductivity, the stainless steel may be coatedwith a layer of a conductive material such as copper or gold. Althoughstainless steel may not offer the same conductivity as other metals, itdoes offer strength required to puncture tissue and/or skin.

[0065]FIGS. 2A and 2B show an end view and a cross-sectional view,respectively, of a conventional dipole microwave antenna assembly 30. Asseen, antenna assembly 30 has a proximal end 32 which may be connectedto a feedline 14, as further discussed herein, and terminates at distalend 34. The radiating portion of antenna 30 comprises proximal radiatingportion 36 and distal radiating portion 38. Proximal radiating portion36 may typically have an outer conductor 42 and an inner conductor 44,each of which extends along a longitudinal axis. Between the outer andinner conductors 42, 44 is typically a dielectric material 46 which isalso disposed longitudinally between the conductors 42, 44 toelectrically separate them. A dielectric material may constitute anynumber of appropriate materials, including air. Distal portion 48 isalso made from a conductive material, as discussed below. Proximal anddistal radiating portions 36, 38 align at junction 40, which istypically made of a dielectric material, e.g., adhesives, and are alsosupported by inner conductor 44 which runs through junction opening 50and at least partially through distal portion 48. However, as discussedabove, the construction of conventional antenna assembly 30 isstructurally weak at junction 40.

[0066] In operation, microwave energy having a wavelength, λ, istransmitted through antenna assembly 30 along both proximal and distalradiating portions 36, 38. This energy is then radiated into thesurrounding medium, e.g., tissue. The length of the antenna forefficient radiation may be dependent at least on the effectivewavelength, λ_(eff), which is dependent upon the dielectric propertiesof the medium being radiated into. Energy from the antenna assembly 30radiates and the surrounding medium is subsequently heated. An antennaassembly 30 through which microwave energy is transmitted at awavelength, λ, may have differing effective wavelengths, λ_(eff),depending upon the surrounding medium, e.g., liver tissue, as opposedto, e.g., breast tissue. Also affecting the effective wavelength,λ_(eff), are coatings which may be disposed over antenna assembly 30, asdiscussed further below.

[0067]FIG. 3 shows an exploded cross-sectional view of a variation onpre-stressed antenna assembly 60 made at least in part according to thepresent invention. In making antenna assembly 60, junction member 62 maybe placed about inner conductor 44 through junction opening 64. Distalportion 48 may be placed over inner conductor 44 and then compressedsuch that junction member 62 is placed under a compressive loadgenerated between proximal radiating portion 36 and distal radiatingportion 38 to create pre-stressed antenna assembly 70, as shown in FIG.4. Antenna assembly 70 may have an overall length of about 1.42 inchesand an outer diameter of about 0.091 inches. The pre-stressed loadingcondition on antenna assembly 70 preferably exists when assembly 70 isunder a state of zero external stress, that is, when assembly 70 is notacted upon by any external forces, e.g., contact with tissue, externalbending moments, etc.

[0068] The compression load is preferably first created by feedingdistal portion 48 over inner conductor 44 until junction member 62 isunder compression, then inner conductor 44 is preferably affixed todistal portion 48 to maintain the compression load on junction member62. Some clearance may be necessary between junction member 62 and innerconductor 44 to avoid any interference resistance between the two. Innerconductor 44 may be affixed to distal portion 48 along interface 72 by avariety of methods, such as welding, brazing, soldering, or by use ofadhesives. The compression loading occurs such that while innerconductor 44 is placed under tension along direction 76, distal portion48 places the outer portions of junction member 62 under compressionalong directions 74. Inner conductor 44 may be heated prior to affixingit to distal portion 48 by any number of methods because heating innerconductor 44 may expand the conductor in a longitudinal direction(depending upon the coefficient of thermal expansion of the innerconductor 44).

[0069] For example, heating inner conductor 44 may be accomplishedduring the welding or soldering procedure. Upon cooling, inner conductor44 may contract accordingly and impart a tensile force upon theconductor 44 while simultaneously pulling junction member 62 intocompression. To allow the compression loading to transfer efficientlythrough assembly 70, junction member 62 is preferably made of adielectric material which has a sufficiently high compressive strengthand high elastic modulus, i.e., resistant to elastic or plasticdeformation under a compression load. Therefore, junction member 62 ispreferably made from materials such as ceramics, e.g., Al₂O₃, BoronNitride, stabilized Zirconia, etc. Alternatively, a junction member 62made of a metal and sufficiently coated with a dielectric or polymer maybe used, provided the dielectric coating is sufficiently thick toprovide adequate insulation. To prevent energy from conducting directlyinto the tissue during use, a dielectric layer having a thicknessbetween about 0.0001 to 0.003 inches, may be coated directly overantenna assembly 70. The dielectric coating may increase the radiatedenergy and is preferably made from a ceramic material, such as Al₂O₃,TiO₂, etc., and may also be optionally further coated with a lubriciousmaterial such as Teflon, polytetrafluoroethylene (PTFE), or fluorinatedethylene propylene (FEP), etc. In addition to the dielectric coating, asealant layer may also be coated either directly over the antennaassembly 70, or preferably over the dielectric layer to provide alubricious surface for facilitating insertion into a patient as well asto prevent tissue from sticking to the antenna assembly 70. The sealantlayer may be any variety of polymer, but is preferably a thermoplasticpolymer and may have a thickness varying from a few angstroms to asthick as necessary for the application at hand. Varying these coatingthicknesses over antenna assembly 70 may vary the effective wavelengths,λ_(eff), of the radiation being transmitted by the antenna. Thus, onemay vary the coating thicknesses over the assembly 70 to achieve apredetermined effective wavelength depending upon the desired results.

[0070]FIG. 5 shows another variation of pre-stressed antenna assembly80. This variation also has proximal radiating portion 82 attached todistal radiating portion 84 with junction member 86 therebetween under acompression load, as described above. Proximal radiating portion 82 mayhave outer conductor 88 and inner conductor 92 extending longitudinallywith dielectric material 90 disposed in-between conductors 88, 92.However, this variation shows distal end 94 having distal radiatingportion 84 with tapered end 96 terminating at tip 98, which ispreferably sharpened to allow for easy insertion into tissue. Apreferable method of optimizing the amount of radiated energy fromassembly 80 may include adjusting the length of proximal radiatingportion 82 to correspond to a length of λ/4 of the radiation beingtransmitted through assembly 80, and likewise adjusting a cumulative (oroverall) length of distal radiating portion 84 and junction 86 to alsocorrespond to a length of λ/4. Adjusting the lengths of proximal anddistal radiating portions 82, 84 to correspond to the wavelength of thetransmitted microwaves may be done to optimize the amount of radiatedenergy and accordingly, the amount of the medium or tissue which issubsequently heated. The actual lengths of proximal and distal radiatingportions 82, 84 may, of course, vary and is not constrained to meet aλ/4 length. When antenna assembly 80 is radiating energy, the ablationfield is variable 3-dimensionally and may be roughly spherical orellipsoid and centers on junction 86 and extends to the ends of theproximal and distal radiating portions 82, 84, respectively.

[0071] The location of tip 98 may be proportional to a distance of λ/4of the radiation being transmitted through assembly 80, but because tip98 terminates at tapered end 96, the angled surface of taper 96 may betaken into account. Thus, the total distance along the outer surfaces ofassembly 80 from B to C plus the distance from C to D may accord to thedistance of λ/4. The length of proximal radiating portion 82, i.e., thedistance along the outer surface of assembly 80 from A to B, may alsoaccord to the distance of λ/4, as above. Although it is preferable tohave the length of the radiating portion of the antenna accord with adistance of the wavelength, λ, it is not necessary for operation of thedevice, as described above. That is, an antenna assembly having aradiating portion with a length in accordance with a first wavelengthmay generally still be used for transmitting radiation having a secondwavelength, or third wavelength, or so on, although with a possiblereduction in efficiency.

[0072]FIG. 6 shows an exploded cross-sectional view of another variationon pre-stressed antenna assembly 100. Assembly 100 shows a variation ofjunction member 102 which has a radial thickness which is non-uniformabout a longitudinal axis as defined by junction member 102. Theproximal portion is comprised of outer conductor 110, inner conductor112, dielectric material 114, as above. However, junction 102 is shownin this variation as a stepped member having at least two differentradiuses. In other variations, the junction may be curved or havemultiple steps. Central radius 104 of junction member 102 is shown ashaving a diameter similar to that of outer conductor 110 and distalportion 120. Stepped radius 106, which is preferably smaller thancentral radius 104, may be symmetrically disposed both proximally anddistally of central radius 104. To accommodate stepped junction member102 during the assembly of antenna 100, receiving cavity 116 may be madein dielectric material 114 and receiving cavity 118 may be made indistal portion 120 to allow for the interfitting of the respectiveparts. Such a stepped design may allow for the compression load to beconcentrated longitudinally upon the central radius 104 of junctionmember 102 to allow for the efficient transfer of the load along theproximal portion.

[0073] In addition to stepped junction member 102, FIG. 6 also showschannel 122 extending longitudinally from distal tip 124 to receivingcavity 118. Once inner conductor 112 may be placed through junctionopening 108 and into distal portion 120, either partially or entirelytherethrough, channel 122 may allow for access to inner conductor 112for the purpose of affixing it to distal portion 120. Affixing innerconductor 112 may be done to place it under tension by any of themethods as described above, such as welding or soldering.

[0074] However, having channel 122 extend from the distal tip 124 toinner conductor 112 may limit the sharpness of tip 124. Accordingly,variation 130 in FIG. 7 shows an alternate distal end 132 which defineschannel 138 for receiving inner conductor 92 but which also definesaccess channel 140 extending from a side surface of distal end 132 tochannel 138. Access channel 140 allows for access to inner conductor 92to affix it to distal end 132 while allowing for tapered end 134 toterminate at sharpened tip 136. Although a single channel is shown inthis variation, multiple channels may be incorporated into the design atvarious locations.

[0075] While most of the variations described above are related todipole antenna assemblies, FIG. 8 shows monopole antenna assembly 150made at least in part according to the present invention. As shown,there may be a single radiating portion 152 which preferably has alength corresponding to a length of λ/2, rather than λ/4, of theradiation being transmitted through assembly 150. As above, monopoleassembly 150 may apply a compressive load upon junction member 154between radiating portion 152 and proximal end 156. The principles ofhaving an antenna length correspond to a length of λ/2 or λ/4, as wellas having tapered distal ends or tips on the distal portion, may beutilized not only with antennas assembled using compression methods, butthese principles may be used with any of the variations describedherein.

[0076] To improve the energy focus of an antenna assembly, an electricalchoke may also be used to contain returning currents to the distal endof the antenna. Generally, the choke may be disposed on the antennaproximally of the radiating section. The choke is preferably placed overa dielectric material which may be disposed over the antenna. The chokeis preferably a conductive layer and may be further covered by a tubingor coating to force the conductive layer to conform to the underlyingantenna, thereby forcing an electrical connection (or short) moredistally and closer to the radiating section. The electrical connectionbetween the choke and the underlying antenna may also be achieved byother connection methods such as soldering, welding, brazing, crimping,use of conductive adhesives, etc. The following description is directedtowards the use of a choke on a compression antenna variation forillustration purposes only; however, the choke may also be used with anyof the antenna variations described below.

[0077]FIG. 9A shows a side view of a variation on pre-stressed antennaassembly 160 with an electrical choke and FIG. 9B shows cross-sectionedside view 9B-9B from FIG. 9A. Similar to the antenna assemblies above,assembly 160 shows radiating portion 162 electrically attached viafeedline (or shaft) 164 to a proximally located coupler 166. Detail 174of radiating portion 162 and detail 180 of feedline 164 are described infurther detail below. Radiating portion 162 is shown with sealant layer168 coated over section 162. Electrical choke 172 is shown partiallydisposed over a distal section of feedline 164 to form electrical chokeportion 170, which is preferably located proximally of radiating portion162. Details 176, 178 of choke portion 170 are described in furtherdetail below.

[0078]FIG. 10 shows detailed view 174 from FIG. 9B of a variation on apre-stressed antenna section. As seen, distal radiating portion 190 andproximal radiating portion 192 are located in their respective positionsabout junction member 194, which in this variation is shown as a steppedmember. Proximal radiating portion 192 is further shown having outerconductor 196 preferably disposed concentrically about inner conductor198 with dielectric 200 placed in between outer and inner conductors196, 198 for insulation. Inner conductor 198 may be fed through junctionmember 194 and into distal radiating portion 190 to be affixed by weldor solder 202 to distal radiating portion 190 via access channel 204,which is shown to extend from a distal end of inner conductor 198 to anouter surface of portion 190. As described above, inner conductor 198may be heated to longitudinally expand it prior to affixing it to distalportion 190. As inner conductor 198 cools, a tensile force is impartedin inner conductor 198 which draws the distal and proximal portions 190,192 together longitudinally. In turn, this imparts a compressive forceupon the radial portions of junction member 194, preferably at thejunction-to-distal portion interface 206. Optionally, dielectric layer208, which may be a ceramic material such as Al₂O₃, may be coated overthe radiating antenna portion. Moreover, a lubricious layer such asTeflon, may also be coated over the antenna portion as well along withdielectric layer 208. A further sealant layer 210 may optionally becoated over dielectric layer 208 as well. Sealant layer 210 may be madefrom a variety of thermoplastic polymers, e.g., heat shrink polymers,such as polyethylene (PE), polyethylene terephthalate (PET),polytetrafluoroethylene (PTFE), fluorinated ethylene propylene (FEP),perfluoroalkoxy (PFA), chlorotrifluoroethylene (CTFE), ethylenechlortrifluoroethylene (ECTFE), and ethylene tetrafluoroethylene (ETFE).The description is directed towards the use of dielectric and sealantlayers on a compression antenna variation for illustration purposesonly; however, the uses of dielectric and sealant layers may also beused with any of the antenna variations described below.

[0079]FIG. 11 shows detailed view 176 from FIG. 9B of a variation on thetransition to electrical choke portion 170. Electrical choke 172 may bedisposed proximally of sealant layer 210 or proximal radiating portion192. Although shown with a gap between choke 172 and sealant layer 210in this variation, the two may touch or overlap slightly. FIG. 12 showsa more detailed view 178 of the various layers which may compriseelectrical choke 172. In this variation, a first inner dielectric layer220 may be disposed over the antenna assembly. The first innerdielectric layer 220 may be made from any of the various thermoplasticpolymers, ceramics, or other coatings, as described above. A secondinner dielectric layer 222 may optionally be disposed over first innerdielectric layer 220 and may be made from the same or similar materialas first inner dielectric layer 220. Conductive layer 224 may then bedisposed over the dielectric layers. Conductive layer 224 is preferablya conductive coating, a conductive foil material, e.g., copper foil, ora metal tubing and electrically contacts outer conductor 196 at somelocation along choke 172 proximally of radiating portion 162.

[0080] Variation 160 illustrates electrical contact between conductivelayer 224 and outer conductor 196 in detail 178 occurring at theproximal location of electrical choke portion 170, but choke 172 may beformed without forcing contact between outer conductor 196 with layer224 provided the length of choke 172 is chosen appropriately. Forinstance, choke 172 having a sufficiently long length, e.g., a length ofλ/2, may be used without having to force contact between the layers.Outer dielectric layer 226 may be disposed upon conductive layer 224.Outer dielectric layer 226 may also be made of any of the variouspolymers as described above and is preferably a heat shrinkable layerthat may force conductive layer 224 to conform more closely to theunderlying layers to not only force a better electrical connection, butalso to reduce the overall diameter of the antenna section. FIG. 13shows detailed view 180 from FIG. 9B of a variation on the feedline. Asshown, feedline 164 may be a simple coaxial cable where outer conductor196, inner conductor 198, and dielectric 200 extend throughout thefeedline. Outer dielectric layer 226 may also extend down over feedline164 and even over the entire antenna assembly.

[0081] Further steps may optionally be taken to further increase thestrength of an antenna assembly by altering any of the layers, such assealant layer 210 or any of the other heatshrink layers discussed above.FIG. 14 shows one example of antenna section 230 where wires or strands236 may be formed within or on the layers 232 to add strength. The wires236 may be formed within the layer 232 and are preferably orientatedlongitudinally along the length of antenna section 230 such that thebending strength of the antenna is increased. The layers 232 may beformed over outer conductor 234, as described above, and wire 236 may bemade of any high-strength material, e.g., Kevlar, metals, etc. Metalwires may be used provided they are well insulated by layers 232.

[0082] Antenna Assembly Via Mechanical Fastening

[0083] Aside from using a compressive load to increase antenna strength,as described above, alternative methods may be employed for increasingantenna strength to withstand direct insertion into tissue. Analternative variation may include assembling an antenna using mechanicalfastening methods. FIG. 15, for example, shows a cross-sectionedvariation of a mechanically threaded interface or “screw-on” variation240 as an exploded assembly. As seen, proximal portion 242 may beconnected to distal portion 244 by using a junction member 246 havingfirst and second junction mating sections 252, 254, respectively.

[0084] Junction member 246 is preferably comprised of any of thedielectric materials as described above. Alternatively, a dielectriccoating or layer may also be applied to the inside of channels 248, 260which contacts junction member 246. First and second mating sections252, 254 may be threaded 256, 258, respectively, such that the threadpitch on each section 252, 254 is opposed to each other, i.e., the pitchangle of threading 256 may be opposite to the pitch angle of threading258. Alternatively, the thread pitch on each section 252, 254 may beconfigured to be angled similarly for ease of antenna assembly. Proximalportion 242 may have a receiving cavity or channel 248 which is threaded250 at a predetermined pitch to correspond to the pitch and angle of thethreading 256 on first mating section 252. Likewise, distal portion 244may have a receiving cavity or channel 260 which is threaded 262 at apredetermined pitch to correspond to the pitch and angle of thethreading 258 on second mating section 254. Having opposed pitch anglesmay be done to ensure a secure fit or joint when variation 240 isassembled by screwing proximal portion 242 and distal portion 244together onto junction member 246.

[0085] A further screw-on variation 270 is shown in FIG. 16. Here,proximal portion 272 may have a proximal mating section 274 which isthreaded 276 at a predetermined pitch and angle to correspondingly screwinto distal portion 282 via threaded receiving channel 278. Channel 278preferably has threading 280 which matches threading 276 on matingsection 274 to ensure a tight fit and a secure joint. Although variation270 shows a mating section 274 on proximal portion 272 and receivingchannel 278 in distal portion 282, a mating section may instead belocated on distal portion 282 for insertion into a correspondingreceiving channel located in proximal portion 272. Preferably, adielectric coating or layer 284 is applied either to the inside ofchannel 278 or on the outer surface of mating section 274 as shown (orupon both) to prevent contact between proximal and distal portions 272,282, respectively.

[0086] Antenna Assembly Via Overlap

[0087] Another variation on assembling an antenna is by use ofoverlapping or interfitting joints to attach proximal and distalportions together. FIG. 17 shows a crimped or overlapping variation 290.Proximal portion 292 is preferably attached to distal tip or portion 294by inner conductor 302 and by having a distal end section of theproximal portion 292 crimped and portion 294 maintained in position viaa molded material 300, which is also preferably dielectric such as abiocompatible thermoset plastic or polymer (including any of thedielectric materials discussed herein). The distal end section, i.e.,crimped dielectric 296 and crimped outer conductor 298, is preferablycrimped or tapered in a reduced diameter towards the distal end while aportion of dielectric 296 near crimped outer conductor 298 may bepartially removed to allow for material 300 to be formed within, asshown in the figure. While the inner conductor 302 is held betweenproximal and distal portions 292, 294, respectively, the moldablematerial 300 may be injection molded within a die or preform holding theassembly to form a unitary structure with both portions 292, 294.Material 300 may also be shaped into various forms depending upon thedesired application, such as a tapering distal end, as shown in the FIG.17.

[0088]FIG. 18 shows another variation 310 where proximal portion 312 ispreferably configured to receive and hold distal portion 314. Proximalportion 312 may have a distal section of dielectric material 316 removedpartially to create a receiving channel 318 within portion 312. Distalportion 314 may be snugly placed within this channel 318 such thatportion 314 is partially within and partially out of dielectric material316, as shown. A layer 320 of the dielectric material 316 may be leftbetween outer conductor 322 and distal portion 314 to form an insulativebarrier between the two. Alternatively, dielectric layer 320 may beformed of a different material than dielectric 316. To further aid inantenna 310 insertion into tissue, the distal end of distal portion 314,as well as the distal end of outer conductor 322, may be tapered tofacilitate insertion. The overlapping segment between proximal anddistal portions 312, 314, respectively, may be varied depending upon thedesired bending resistance and desired strength of antenna 310.

[0089]FIG. 19 shows a further variation 330 of an overlapping joint forassembling the antenna. Proximal portion 332 preferably has a matingchannel 340 in the distal end of the portion 332 for receiving matingsection 338 of distal portion 334. This variation 330 preferably has anoverlapping junction member 336 which may be slipped over mating section338 prior to insertion into channel 340. Overlapping junction member 336is preferably a dielectric material and fits snugly between proximalportion 332 and mating section 338 to form an overlapping joint when theinner conductor is attached to distal portion 334, as described above.

[0090]FIG. 20 shows an antenna variation where different methods ofoverlapping attachments may be utilized. Distal portion 350 is shownhaving a cylindrical interfitting member 358. The portion 350 may beinserted via member 358 into a corresponding receiving channel 356preferably defined in the outer conductor of proximal portion 354. Anend view of proximal portion 354 in FIG. 21A shows channel 356 in thisvariation for receiving a cylindrically shaped member 358.

[0091] Another variation is shown in distal portion 352 where ratherthan having a conical interfitting member, separate pins or dowels 360may be used to extend into receiving channels 356′ of proximal portion354′. These pins 360 may be integral with distal portion 352 or they maybe separate members inserted and held in distal portion 352; in eithercase, pins 360 are preferably made of a hard dielectric material or ametal sufficiently coated with a dielectric material for insulation. Asseen in FIG. 21B, which is an end view of proximal portion 354′,channels 356′ are shown located every 90° about portion 354′. Althoughfour pins are used in this variation, any number of pins may be usedranging from two to several depending upon the desired strength of theantenna assembly. To support such a plurality of pins, it may bedesirable to have proximal portions 354, 354′ with an outer conductorhaving a thickness ranging from 0.005 to 0.010 inches.

[0092]FIG. 22 shows an antenna assembly with an overlappinginterference-fitted variation 370. As seen, proximal portion 372 may beattached to distal portion 374 by a junction member 376 which ispreferably interference fitted, i.e., frictionally-fitted, between bothportions 372, 374. The junction member 376 may have a first and a secondsection 382, 384, respectively, which preferably has a diameter D₂.Receiving channel 378 in proximal portion 372 preferably has a diameterD₁ and receiving channel 380 in distal portion 374 also has a diameterD₁ or some diameter less than D₂. Accordingly, diameter D₁ is some valueless than D₂ such that an interference fit is created between junction376 and portions 372 and 374. Accordingly, distal portion 374 isfrictionally held to proximal portion 372.

[0093]FIG. 23 shows another interfitting variation 390 utilizing ajunction member 396 which is preferably held between proximal portion392 and distal portion 394 by multiple pins 398, 402 which may bereceived in channels 400, 404, respectively. Accordingly, as discussedabove, any number of pins 398 extending from proximal portion 392 may beinserted into corresponding channels 400, and any number of pins 402extending from distal portion 394 may likewise be inserted intocorresponding channels 404.

[0094]FIG. 24 shows an overlapping and interfitting variation 410 whereproximal portion 412 has receiving channel 416 for receiving distalportion 414. Within channel 416, there may be a plurality of depressions418 defined in the surface of the outer conductor. These depressions 418are preferably shaped to have a locking configuration, such as a righttriangle shape, when projections 420, which are located radially ondistal portion 414, are inserted into and mated to depressions 418.Projections 420 are preferably protrusions which extend from a surfaceof distal portion 414 and are preferably radially disposed on the outersurface. Also, any number of projections 420, e.g., at least two toseveral, may be utilized but are preferably equally radially spaced fromone another depending upon the desired strength of the overlappingjoint. To facilitate insertion of distal portion 414 into channel 416,projections 420 may be disposed on the ends of a number of correspondingsupport members 422 flexibly attached to distal portion 414. Supportmembers 422 would allow projections 420 to be retracted at leastpartially into the outer surface of distal portion 414 during insertion,and when distal portion 414 is fully inserted into channel 416,projections 420 may then be allowed to expand into and intimately matewith the depressions 418 such that distal portion 414 is held fixedrelative to proximal portion 412. A dielectric material may be coated orsprayed within channel 416 or on distal portion 414 to insulate betweenthe two portions 412, 414.

[0095]FIG. 25 shows a further variation 430 of that shown in FIG. 24.Proximal portion 432 may be attached to distal portion 434 by anoverlapping joint where mating section 438 on distal portion 434 may beinserted into receiving channel 436. Once inserted, distal portion 434may be held to proximal portion 432 by projections 442 intimately matingwithin corresponding depressions 444. Distal portion 434 may be madeentirely of a dielectric material; alternatively, mating section 438 maybe made at least partly of a dielectric while the remainder of distalportion 434 may be metallic. To further ensure a strong joint,depressions 444 may have a number of access channels 440 preferablyextending radially from depressions 444 defined in the surface ofchannel 436 to an outer surface of proximal portion 432. Access channels440 may be used to provide access to projections 442 (once mated withindepressions 444) for further fixation to proximal portion 432 bywelding, soldering, brazing, or by applying adhesives.

[0096] Alternate Methods of Tip or Distal Portion Attachment

[0097] Aside from various methods of assembling microwave antennas,there are also a variety of methods for attaching the tip or distalradiating portion to a remainder of the assembly. The various methodsdescribed below may be used in any of the assembly variations discussedherein depending upon the desired antenna assembly characteristics.

[0098]FIG. 26 shows a partial assembly of a microwave antenna having adistal portion 454 which may be screwed onto the proximal portion 452via the inner conductor 456. The distal end portion of inner conductor456 is preferably threaded 458 on an outer surface. Correspondingly, thereceiving channel 460 within distal portion 454 is likewise threaded toreceive the threaded portion 458 of inner conductor 456. Duringassembly, distal portion 454 may be screwed onto proximal portion 452 byinner conductor 458. Accordingly, the force with which the proximal anddistal portions 452, 454 are held together may be varied by the amountand degree distal portion 454 is screwed or advanced onto innerconductor 456, thereby allowing the rigidity or strength of the antennato be varied according to a desired use or application. In thisvariation, distal portion 454 may be made of a non-metallic material,e.g., a polymer, and attached directly to proximal portion 452;alternatively, distal portion 454 may also be made of a metallicmaterial and used in conjunction with a dielectric junction member, asdescribed above.

[0099]FIG. 27 shows another variation for assembling a distal portion inan isometric exploded view of splittable distal portion 470. The distalportion 470 may be comprised of a splittable distal portion having afirst half 472 and a second half 474. Although shown split into twohalves 472, 474, distal portion 470 may be split into numerous portions,e.g., three or more. Within the adjoining surfaces, anchoring channel476 may be defined to receive inner conductor 480 and may have a portionof channel 476 configured or enlarged to receive an anchoring element482 for holding the inner conductor 480 distal end within distal portion470. Inner conductor 480 preferably has an anchoring element 482 formedon a distal end of inner conductor 480 by rounding or flattening thedistal end into anchoring element 482 or attaching a separate anchoringmechanism onto the distal end. Once inner conductor 480 and anchoringelement 482 are positioned within anchoring channel 476, both halves472, 474 may be attached together, thereby fixedly holding anchoringelement 482 therewithin. When distal portion halves 472, 474 areattached to one another, they may be aligned and positioned relative toeach other by a number of alignment projections 478 on one or bothhalves 472, 474 and the halves may then be held to one another by anynumber of methods, e.g., welding, brazing, soldering, adhesives,snap-fits, etc.

[0100] Another variation for attaching the distal portion is shown inFIG. 28, which is an exploded side view of multi-sectioned portion 490.The distal portion may be comprised of multiple sections which may beinterfitted to form the distal portion. Thus, while proximal portion 492and junction member 494 (which may or may not be used in this variation)are assembled as in some of the other variations, the distal portion mayhave a first section 496 through which inner conductor 506 may be passedthrough via access channel 502. Once the distal tip of inner conductor506 is passed through junction member 494 and access channel 502, it maythen be attached to first section 496 at the end of access channel 502by any of the attachment methods described above. First section 496 maythen be assembled with second section 498 by interfitting mating section500 into receiving channel 504. The use of a multi-sectioned portionsuch as that shown in portion 490 may enable one to first attach theproximal portion with the distal portion and variably alter the tip ofthe distal portion according to a desired application.

[0101] To further aid in tip or distal portion attachment to the antennaassembly, various distal portions may be used to facilitate assembly anduse in a patient. As previously described, the distal tip is preferablytapered and terminates at a tip to facilitate antenna insertion intotissue with minimal resistance. Also, attaching the inner conductor tothe distal portion may be facilitated by an access channel defined inthe distal portion so that the inner conductor may be attached bywelding, soldering, etc. within the distal portion. To furtherfacilitate this assembly process, the distal tip may be formed into anarcuate or curved face terminating into a tip, as seen in FIG. 29. Asshown in the cross-sectional side view of alternate tip 510, it may havethe arcuate or curved face 512 sloping distally such that tip 514 isformed off-center from the longitudinal axis defined by the antenna towhich alternate tip 510 may be attached. Accordingly, inner conductor518 may be routed through access channel 516 and then attached by any ofthe methods described to alternate tip 510 thereby allowing tip 514 tobe sharpened as necessary and allowing an access channel 516 to bemaintained along the longitudinal axis of the antenna for ease ofassembly.

[0102] Alternate Distal Portion Attachments

[0103] As discussed above, the energy with a wavelength, λ, istransmitted down a microwave antenna and is subsequently radiated intothe surrounding medium. In operation, microwave energy having awavelength, λ, is transmitted through the antenna assembly along bothproximal and distal radiating portions. This energy is then radiatedinto the surrounding medium. The length of the antenna for efficientradiation may be dependent at least on the effective wavelength,λ_(eff), which is dependent upon the dielectric properties of the mediumbeing radiated into. Energy having the effective wavelength radiates andthe surrounding medium is subsequently heated. An antenna assemblythrough which microwave energy is transmitted at a wavelength, λ, mayhave differing effective wavelengths, λ_(eff), depending upon whetherthe energy is radiated into, e.g., liver tissue, as opposed to, e.g.,breast tissue. Also affecting the effective wavelength, λ_(eff), arecoatings which may be disposed over the antenna assembly.

[0104] Accordingly, various distal portions having varying diameters areshown in FIGS. 30 to 32. FIG. 30, for instance, shows a representativeantenna 520 having a constant diameter from proximal portion 522 todistal portion 524 while covered with an optional heatshrink 526, asdescribed above, for comparison purposes. FIG. 31 shows antenna 530having distal portion 532 with a larger diameter than proximal portion522. Heatshrink 526 in this variation may be desirable to smooth thetransition between the different diameters. On the other hand, FIG. 32shows antenna 540 having distal portion 542 with a diameter that issmaller than that of proximal portion 522. Having heatshrink 526 in thisvariation may also be desirable to likewise smooth the transitionbetween the different diameters. Varying the diameters of the distalportion may change the radiative properties of the effective wavelengthin addition to the different medium types being radiated into.Accordingly, the diameter of the distal portion may be varied to give adesired radiative effect for different tissue types. Besides thediameter of the distal portion, the thicknesses of heatshrink 526 or anyof the other dielectric and sealant layers, as described above, may alsobe varied accordingly in addition to the distal portion diameter.Although only two variations are shown in FIGS. 31 and 32, the distaltips may have a variety of configurations; for instance, it may bestepped, ramped, tapered, etc., depending upon the desired radiativeeffects.

[0105] Antenna Deployment

[0106] As described above, the microwave antenna may be inserteddirectly into the tissue and into the lesion to be treated. However,during insertion, the antenna may encounter resistance from some areasof tissue, particularly in some tissue found, e.g., in the breast. Whenthe microwave antenna encounters resistance, if force were applied,tissue damage may result or the target tissue may be inadvertentlypushed away due to the differential density of the target tissuerelative to the surrounding tissue. Therefore, RF energy may also beutilized with the microwave antenna for facilitating deployment withinthe tissue.

[0107] In use, the RF energy may be simply left on the entire time theantenna is advanced through the tissue, or it may be applied or turnedon only as needed as the antenna encounters resistance from the tissue.With the RF energy activated, the antenna may be further advancedutilizing the RF energy to cut through the obstructive tissue. Once theantenna has been desirably positioned within a lesion or region oftissue, the RF energy, if on, may be switched off and the microwaveenergy may be switched on to effect treatment.

[0108] One variation of antenna assembly 550 is shown in FIG. 33.Assembly 550 may use RF energy at the distal tip of the antenna as acutting mechanism during antenna deployment. The microwave antenna 552is preferably covered with some insulative material 554 along most ofits length, but distal tip 556 may be uninsulated such that the RFenergy may be applied thereto through the inner conductor. To utilizethe RF energy cutting mechanism at the distal tip, the inner conductormay be made from Nitinol, Tungsten, stainless steel, or some otherconductive metal.

[0109] Antenna 552, through cable 558, may be electrically connected toan RF generator 564 which provides the RF energy to distal tip 556during placement and positioning of antenna 552 within the tissue orlesion. After antenna 552 has been desirably positioned within thelesion, connector 560 may be disconnected from RF cable 562 and attachedto a microwave generator 568 via microwave cable 566 to provide themicrowave energy for effecting treatment to the tissue.

[0110] Alternatively, given the small amount of surface area of distaltip 556, a low power RF generator may be utilized and can be built intoan integral unit 568 along with the microwave generator. Alternatively,the optional RF generator 564 may be physically separated from themicrowave generator and may be electrically connected as a separateunit, as shown.

[0111] Another variation on antenna assemblies utilizing RF energy isshown in FIGS. 34A and 34B. In this variation, antenna assembly 570 mayhave antenna body 572 define a lumen 574 therethrough within which innerconductor 576 may be slidingly positioned. During insertion of theantenna into the tissue, distal tip 578 may be used to pierce throughthe tissue, as seen in FIG. 34A. When resistance is encountered, innerconductor 576 may be advanced distally through lumen 574 to extend atleast partially out of distal tip 578. To facilitate movement of innerconductor 576 within antenna 572, the inner surface of lumen 576 may becoated with a lubricious material or the outer surface of innerconductor 576 may alternatively be coated. If inner conductor 576 iscoated, a distal end portion of inner conductor 576 may be left exposedsuch that RF energy may be delivered through the inner conductor 576 atthis exposed end. To optimize the microwave radiation transmitted fromantenna assembly 570, electrical choke 573 may be disposed partiallyover antenna body 572, as shown. Electrical choke 573 may be made andutilized in any of the variations as described in detail above.

[0112] Aside from the illustrations of possible antenna deploymentmethods and devices described above, other variations for deployment andinsertion into tissue may be utilized. Potential other methods anddevices for antenna deployment and insertion may be found in co-pendingU.S. patent application entitled “Microwave Antenna Having A CurvedConfiguration” filed Sep. 15, 2002, which is commonly owned and isincorporated herein by reference in its entirety.

[0113] Methods of Use

[0114] In using a microwave antenna, several different methods may beutilized. FIG. 35A shows an isometric view of one variation 580 in whicha single antenna 582 may be utilized within the tissue. FIG. 35B showsan end view of the antenna 582 and an example of a possible resultingablation field or region 584 using that single antenna 582. In such acase, antenna 582 may be positioned directly within the tissue to betreated.

[0115]FIGS. 36A and 36B show another variation 590 in which a singleantenna 592 may be positioned in one of several locations 592′ and/or592″ about the tissue to be treated. Antenna 592 may be activated in afirst position, then removed and repositioned in a second position 592′and activated, and then removed and again repositioned in a thirdposition 592″ and again activated, and so on. The order of positioning,relative placement, and depth of insertion of the antenna may besequential or varied, and the number of times the antenna is positionedor repositioned within the tissue may also be varied depending upon thedesired ablation effects. This example shows antenna 592 beingpositioned three times for illustrative purposes but the invention isnot so limited. FIG. 36B shows an end view of the overall resultingablation field 594 due to the overlapping individual ablation fields.

[0116] Another variation for antenna use is shown in FIGS. 37A and 37B.This variation shows antenna assembly 600 in which multiple antennas maybe utilized in combination with one another. This example shows first,second, and third antennas 602, 604, 606, respectively, which may beused simultaneously, although any number of antennas may be useddepending upon the desired ablation effects. Additionally, antennas 602,604, 606 are shown in this example positioned in a triangular pattern;however, any variety of patterns may be utilized depending upon thenumber of antennas used and the desired ablation effects. In thisvariation, all three antennas 602, 604, 606 may be turned onsimultaneously to effect an overall larger ablation region. FIG. 37Bshows an end view of an example of a combined ablation field 608 whichmay result when all antennas are on simultaneously. As seen, theindividual antennas may combine to form a larger and more uniformablation field 608.

[0117] In using multiple antennas simultaneously, the energy supplied tothe antennas may alternatively be cycled or pulsed to effect a combinedablation field. Rather than using antennas 602, 604, 606 turned onsimultaneously, they may instead be energized cyclically through the useof multiple channels from a single unit by multiplexing and cycling theoutput. This may eliminate the use of multiple generators since eachantenna would typically require the use of a generator. The effects ofmultiple channel generators, which typically requires the use ofmultiple generators, may be accomplished by using a single generator andmay result in a much lower power consumption. For instance, a threechannel 100 W generator system would otherwise require about three timesthe power, i.e., 300 W, if used by a single channel system if the powerwere produced for each channel simultaneously.

[0118]FIG. 38 schematically shows channel splitter assembly 610 whichmay be used to create multiple channels by using a single source withmultiplexing. A single microwave generator module 618 having, e.g., a100 W output, may create a single channel A. The single channel A may beswitched between several separate channel outputs, A₁ to A_(N) createdby channel splitter 612. Any number of multiple outputs may be useddepending upon the desired number of channels and the desired effects.In use, the output may be cycled through the range of outputs 616through multiple channels A₁ to A_(N) or in any other manner dependingupon the ablation field to be created. Moreover, the rate of cycling mayrange anywhere from several microseconds to several seconds over atreatment period of several minutes or longer.

[0119] Controller 614, which is preferably in electrical communicationwith channel splitter 612 may be used for several purposes. It may beused to control the cycling rate as well as the order of channels inwhich the output is cycled through. Moreover, controller 614 may be anautomatic system or set by the technician or physician. An automaticsystem may be configured to detect the electrical connection to theantenna and to control the delivery of the energy to the antenna. Thedetection may be achieved by either a passive or active component in thesystem which may monitor reflections from the antenna to determinewhether a proper connection is present. A controller set by thetechnician or physician may be configured to require manual initiationfor energy delivery to begin.

[0120] The applications of the antenna assemblies and methods of makingthe assemblies discussed, above are not limited to microwave antennasused for hyperthermic, ablation, and coagulation treatments but mayinclude any number of further microwave antenna applications.Modification of the above-described assemblies and methods for carryingout the invention, and variations of aspects of the invention that areobvious to those of skill in the art are intended to be within the scopeof the claims.

We claim:
 1. A method for delivering microwave energy therapycomprising: positioning a first microwave antenna in a first position inor near a region of tissue to be treated; positioning at least a secondmicrowave antenna in a second position in or near the region of tissueto be treated; applying microwave energy to the first and secondmicrowave antennas such that a combined ablation region is created aboutthe antennas for treating the region of tissue.
 2. The method of claim 1further comprising providing a first microwave antenna prior topositioning the antenna, the first microwave antenna comprising aproximal portion having an inner conductor and an outer conductor, eachextending therethrough, the inner conductor disposed within the outerconductor; and a distal portion attached to the proximal portion suchthat the inner conductor extends at least partially therein, whereineach of the proximal and distal portions are configured to mate togethersuch that the proximal and distal portions are fixedly positionedrelative to one another by a mechanically engaging joint coupling thedistal portion to the proximal portion.
 3. The method of claim 1 furthercomprising positioning a plurality of additional microwave antennas inor near the region of tissue to be treated prior to applying themicrowave energy.
 4. The method of claim 3 wherein the plurality ofadditional microwave antennas are positioned in a triangular pattern inor near the region of tissue to be treated.
 5. The method of claim 1wherein applying microwave energy comprises simultaneously applyingmicrowave energy to the first and second microwave antennas.
 6. Themethod of claim 1 wherein applying microwave energy comprisessequentially applying microwave energy to the first and second microwaveantennas.
 7. The method of claim 6 wherein the microwave energy isapplied sequentially via a channel splitter in electrical communicationwith a microwave energy generator.
 8. The method of claim 6 furthercomprising cycling the microwave energy between at least the first andsecond microwave antennas.
 9. The method of claim 1 wherein positioningthe first microwave antenna comprises applying RF energy to a distal endof the first microwave antenna.
 10. The method of claim 1 whereinpositioning at least the second microwave antenna comprises applying RFenergy to a distal end of at least the second microwave antenna.
 11. Themethod of claim 1 wherein at least the second microwave antenna ispositioned parallel to the first microwave antenna.
 12. A microwaveantenna system for applying microwave energy therapy comprising: atleast one microwave antenna comprising a proximal portion having aninner conductor and an outer conductor, each extending therethrough, theinner conductor disposed within the outer conductor, and a distalportion attached to the proximal portion such that the inner conductorextends at least partially therein; an energy generator in communicationwith a proximal end of the microwave antenna; and a channel splitter inelectrical communication with the microwave energy generator, whereinthe channel splitter is adapted to create multiple channels from asingle channel received from the energy generator.
 13. The system ofclaim 12 further comprising a controller in electrical communicationwith the channel splitter for controlling a cycling rate of the channelsplitter.
 14. The system of claim 13 wherein the controller is furtheradapted to detect whether an electrical connection to the antenna ispresent.
 15. The system of claim 12 wherein the energy generatorcomprises a microwave energy generator.
 16. The system of claim 12wherein the energy generator comprises an RF energy generator.
 17. Thesystem of claim 12 wherein the distal portion has an insulative coatingover at least a majority of the distal portion and wherein a distal tipis uncovered by the insulative coating.
 18. The system of claim 12wherein the inner conductor is slidingly disposed within the outerconductor such that a distal portion of the inner conductor is distallyextendable past the distal portion.
 19. The system of claim 12 whereineach of the proximal and distal portions are configured to mate togethersuch that the proximal and distal portions are fixedly positionedrelative to one another by a mechanically engaging joint coupling thedistal portion to the proximal portion.